Difference Between Resistance and Capacitance

Posted on September 17, 2011 by admin Last updated on: September 17, 2011

Resistance vs Capacitance

Capacitance and resistance are two of the most fundamental concepts in electronics. These two ideas play a vital role in almost every electronic device we use today. It is particularly beneficial to have a clear understanding in these topics. This article will discuss the differences and similarities between these two topics.

Resistance

Resistance is a fundamental property in the field of electricity and electronics. The resistance in a qualitative definition tells us how hard it is for an electrical current to flow. In the quantitative sense, the resistance between two points can be defined as the voltage difference that is required to take a unit current across the defined two points. Electrical resistance is the inverse of electrical conduction. The resistance of an object is defined as the ratio of the voltage across the object to the current flowing through it. The resistance of a conductor depends on the amount of free electrons in the medium. The resistance of a semiconductor mostly depends on the number of doping atoms used (impurity concentration).

The resistance a system shows to an alternating current is different from that to a direct current. Therefore, the term impedance is introduced in order to make AC resistance calculations much easier. The Ohm’s law is the single most important law when the topic resistance is discussed. It states that, for a given temperature, the ratio of voltage across two points to the current passing through those points is constant. This constant is known as the resistance between those two points. The resistance is measured in Ohms.

Capacitance

The capacitance of an object is a measurement of the amount of charges that object can hold without discharging. Capacitance is an important property in both electronics and electromagnetism. Capacitance is also defined as the ability to store energy in an electric field. For a capacitor which has a V voltage difference across the nodes, and the maximum amount of charges that can be stored in the system is Q, the capacitance of the system is Q/V, when all are measured in SI units. The unit of capacitance is farad (F). However, it is inconvenient to use such a large unit. Therefore, most of the capacitance values are measured in nF, pF, µF and mF ranges.

The energy stored in a capacitor is equal to (QV2)/2. This energy is equal to the work done on each and every charge by the system summed up. The capacitance of a system depends on the area of the capacitor plates, the distance between the capacitor plates and the medium between the capacitor plates. The capacitance of a system can be increased by increasing the area, or decreasing the gap, or having a medium with higher dielectric permittivity.

What is the difference between Resistance and Capacitance?

• Resistance is a value of the material itself while capacitance is a value of the combination of objects.

• Resistance depends on temperature while capacitance does not.

• Resistors behave similarly to both AC and DC but capacitors act in two different manners.